Method of preparing a titanium pigment



0 titanium onto or combined are used to reduce thetime.

washed; while t main behind as pigment properti Patented Sept. 7, 1937 UN TED STATE METHOD or PREPARING a TITANIUM ric- MENT "Beniaminwilson Allan,

to American Md.. a corporati No Drawing.

and

more particularly um dioxide pigments unusual whiteness, extreme soft;- i soluble salts. Speitanium pigments which are produced by calcina fluorine compounds not v stages of calcination.

Titanium dioxide is 9.

tion in the presence of olatile during the early pigment of outstanding value, because of its relative inertness and highopacity. It of methods;

prepared'by'the c raw'hydrated titan common use, the pigme drolytic precipi salts (particula has been prepared but in all cases, 1:

precipitate is always a more ,by a large number he final product, is alcination of a precipitate of lo oxide. In the methods in nt is obtained by the hytation of solutions of titanium rly. titanium sulphate) and the or less hydrated oxide; containing some acid adsorbed with the precipitate.

This precipitate is washed, dried and calcined to remove the water and of the precipitate other pigment properties. When-titanium oxide to temperatures in the water and acid are driven off,

d only with prolonged heating, ercalcination, with the produc which ishard and'gritty, difli in opacity and dirty in color. called conditioning agents have ination of the theory that the acid, and to change to bring up' the: opacitythe range precipitates a. heated from 700-1000 but the acid is acid, whereby overcalcination is acid addition agents leave soluble effect of .basic 0 the alkali bases bases.

Much better of alkali metal to be of assistance pigment properties.

ning agents suggested 15- ompounds, on "the is thereby neutralized. These or insoluble sulphatesin the pigment. It is impossible to cornpletely eliminate calcined pigment is wet the soluble sulphates,'even if the ground, and carefully he insoluble sulphates always re vdiluents to reduce es. In addition, ds, as such,

the desirable the beneficial is rather small,

being far superior to the other results are obtained withthe class ds, as described by Blumcompoun Unfortunately,

#1302593, Januthe resulting calthe structure and fore calcination,

Baltimore, Md., assignor Zirconium Corporation, Baltimore, on .of Maryland Applicat'on March 15, .1935, I Serial N0. 11,294

5 Claims. (01. 134-58) This invention relates to the 'manufacture of titanium' dioxide pigments to the manufacture oititani characterized by 5 ness of texture and absence 0 cifically, it relatesto t contains soluble alkali metal compounds, which are largely used in practice today.

- I have discovered that if the fluorine be added to the pigment before calcination in such form as to be non-volatile during improve the pigment properties the early stages of cal- I ATENT O -I E} f cannot be removed com- 'cination, the fluorine compound acts as a conditioning agent, apparently reacting with the pig ment to form fluortitanic acid, which appears to be the active conditioning agent. The reaction takes place variously during the early stages of calcination, pound used. fluorides are Where metallic fluorides or oxyused, they form H2Fz with theacid present in the raw pigment cake, as the tempera ture 'or the mass is raised in the calciner from room temperatures; this reacts with the TiOa-as As the temperature rises,- Reaction 2 reverses itepending on the particular comments are obtained which are whiter and softer Y than the prior art products, the opacity being similar to that obtained by the 'use of alkali compounds. I a i Two outstanding advantages in operation, in addition to the improved pigment properties, are possible by theuse of fluorine. First, the tendency to overcalcination is reduced to such an extent that, more latitude in this regard can be allowed -in plant operations, both as to time and temperature, in distinction to the necessity for careful control in prior 'art practice. Second,'if the fluorine is added in combination with an element whose oxide or'sulfateis insoluble, nowashing is required, as nosoluble salts need be present asin the case of alkali com und conditioning agents.

I prefer to .add myfluorine to the pigment slurry obtained from the hydrolysis step. lust bel modifications are possible without soluble fluoride, oxyfluoride or fluortitanate. If a volatile fluorine compound is used, such as hydrofluoric acid, or ammonium fluoride. it is necessary to allow suflicient time for a reaction before reaching the volatilization temperature, to permit. reaction with the titanium or other material prescut to fix the fluorine, and prevent premature volatilization. Hydrofluo'ric acid reacts fairly rapidly to form a titanium fluorine compound in which the fluorine is fixed; but with ammonium fluoride, care must be taken to obtain a reaction. as it is relatively unreactive in the slurry.

To illustrate my invention, the following ex amples are cited, it being understood'that various departing from v the spirit of my invention. v

Example 1 To, 100 grams of titanium dioxide in a slurry (prepared by the hydrolysis of a titanium sulphate solution obtained from ilmenite) I added 1 gram of hydrofluoric acid, in 60% aqueous solution. The mixture was stirred thoroughlyfland excess liquid was separated by filtration. The

' precipitate was then calcined in an open muflie The treatment of Example 1 was duplicated, using 3 grams-of hydrofluoricacid. The pigment was similar to that obtained in Example 1, but 40 somewhat softer and of slightly-higher tinting strength. Y Example 3 The treatment of Example 1 was duplicated using 5 grams of hydrofluoric acid. The pigment was extremely soft, andas compared with Example 1, the tinting strength-was about 10% higher.

Example 4 The composition of'Example 3 was calcined in an open muflle for*2 hours at 1050 C. The pigment was similar tothat of Example 3:

A similar pigment slurry was. calcined after adding 2% KzCOa at 1050 C. for 2 hours. The

pigment obtained was rather bluish grey in shade, much harder than the fluorine treated v material, although stillsatisfactory as to texture. It gave an extremely alkaline reaction with bromthymol blue. The same composition, calcined at 850 C. was softer than the over-calcined material, less alkaline, and much whiter in color, although not as white as the fluorine treated pigment.

' Examples A slurry of 100 grams titanium dioxide was mixed with titanium fluoride solution equivalent to 3 grams of HzF'r. The mixture was calcined; for 2 hours at 950 C. The pigment properties were very similar to those obtained in Example'2.

Increasing percentages of titanium fluoride act like increasing percentages of H21: improving softness and slightly bettering tinting strength and color. I

' Example 6 A solution of fluortitanicacid equivalent to 2 thus facilitates fixation. v

I prefer to add the fluorine in such form as'to grams of HzF': was added to 100 grams of titanium dioxide in a typical hydrolysis slurry, and calcined at 950 C. for 2 hours. The product was similar to that of Example 5.

Example 7 Calcium fluoride equivalent to 1% H2Fz. was suspended in a slurry similar to that of Example 6, and excess liquid removed by filtration. The product obtained on calcination at 950 C. for two hours was similar to that of Examples 5 and 6, except that the pigment was slightly alkaline to bromthymol blue.

Zinc fluoride, similarly substituted, gave similar results.

Example 8 Sodium and potassium fluoride were substiq tuted in equivalent quantity, for the fluortitanic Example 10 When ammonium fluoride was substituted in Example 2, no beneficial results were obtained. When the equivalent of 4 grams of HzFa were used, and the slurry was stirred for minutes before calcination, an improvement in properties was noted, the pigment being approximately like that of Example 1.

Example 11 The experiment of ,Example 2 was repeated, with the introduction 'of 1 cc. of N/10 potassium permanganate solution. The pigment calcined after addition of 3 grams H2F2 was practically the equivalent of the pigment produced in the absence of manganese; the pigment produced without treatment was much yellower than in the absence 'of manganese. I attribute this startling improvement to the formation of a white manganese fluorine-titanium compound.

As shown by theexamplea where soluble compounds Of titanium are used, the slurry should preferably not be filtered, to avoid loss of fluorine; with insoluble fluorine compounds, the slurry may be flltered or not, as desired. g

The flxation of the fluorine is of considerable importance. Even though HzFz is extremely reactive, it is not as efficient as its equivalent in fixed salts, apparently because it is prematurely lost in calcination; while ammonium fluoride, being volatile and rather unreactive, requires preliminary treatment to prevent its entire escape. The presence of acid in the pigment cake before or during calcination helps in the formation of the titanium fluorine compounds (probably fluortitanic acid) which are formed,-and

get a neutral pigment, free of soluble salts; hy-

. drogen fluoride, fluortitanic acid, and titanium fluoride or oxyfluoride, are all in this preferred slurry has, of course, a'considerable effect on the group.

The method of preparing the titanium oxide pigment properties of the resultant calcined product; but. my method may be used with any titanium oxide pigment, regardless of method of preparation, to produce improved properties over untreated pigment. I prefer to operate with sulphate or chloride s lutions prepared from ilmenite according to the standard methods now in use, or more preferably according to the co-pending Allan and Bousquet application, Serial #6,!30 tiled February 11, 1935, but I have used other solutions, such as those prepared from rutiie by the method of Richter (U. 8. Patent #1932387, October 24, 1933).

The titanium pigment need not be substantially pure titanium dioxide; but composite pigments comprising titanium dioxide mixed with extenders such as barium and calcium sulphate, or pigments which are largely insoluble titanates, etc. I may be used, and

calcined with improved results in the presence 0! reactable fluorine.

By the use of reactable fluorine in the calcinetion step, I produce ,new titanium pigments, characterized physically by improved color and texture as compared with prior art pigment. high tinting strength, neutrality and freedom from soluble salts if desired.

Various substitutions can be made in the speciflc examples shown, which are merely il1us' trative, without departing from the spirit oi my invention.

I claim:

1. In the production of pigment containing titanium dioxide; the step which comprises calcining a titanium precipitate containing acid, in admixture with fluortitanic acid. using a final calcination temperature oi 700-1050 0.

2. The process of claim 1411 which the fiuortitanlc acid is formed in situ.

3. The process of claim 1 in which the fluortitanlc acid is formed in situ from a fluoride.

4. The process of claim 1 in which the fluortitanlc acid is formed in situ from an oxyfiuoride.

5. In the production of pigment containing titanium dioxide, the step which comprises calcining a titanium precipitate containing acid, in admixture with titanium fluoride, using a final caicination temperature of 100-1050 0.

BENJAMIN WILSON ALLAN. 

